Normothermia is a condition of normal body temperature. Though temperature does vary at different parts of the body, the normal core body temperature of a human adult is often stated to be at 98.6 degrees Fahrenheit or 37.0 degrees centigrade. There are numerous therapeutic reasons for inducing hypothermia (a decrease in the core body temperature), or warming a hypothermic patient to normothermia, or (rarely) to hyperthermia, or inducing normothermia (approximately 37 degrees centigrade) in a patient suffering from an elevated temperature. For example, hypothermia may be induced to minimize damage to the brain or spinal cord when a patient has suffered a head injury or stroke, or to minimize damage to heart and brain tissue when a patient has undergone cardiac arrest or suffered a myocardial infarct (heart attack). Mild hypothermia has been shown to both increase the contractility of the heart muscle and to reduce its metabolic requirements. Indeed, if the hypothermia is systemic, the metabolic demands of the entire body are generally reduced, so that the demands placed on the heart may be reduced. It may sometimes also be desirable to induce hypothermia during surgery, especially neurosurgery, once again to minimize tissue damage.
Cooling is well accepted as a neuroprotectant, and may be helpful for a patient suffering ischemic insult to the brain or spinal cord, such as a stroke or trauma. It is also known that a fever significantly increases the risk of a bad neurologic outcome suffered by a stroke victim. It may therefore be beneficial to cool a stroke victim who would otherwise develop a fever.
Temperature control over a patient may affect the activity of various drugs applied to a patient for therapeutic reasons, such as chemotherapeutic drugs. A physician may wish to control such patient's temperature above or below normothermia. The temperature may also have other therapeutic value, such as reduction of inflammation, or destruction of certain infectious agents such as bacteria or viruses.
In re-warming a patient, either after therapeutic hypothermia or a patient suffering from accidental hypothermia, a very gradual and controlled re-warming rate is often desirable. The dramatic generation of metabolic heat due to shivering, particularly in addition to heat added by other means, can result in rapid and uncontrolled re-warming. A therapeutic regimen for controlling body temperature preferably does so at a carefully monitored and controlled rate.
Early techniques involved application of cold to the skin surface or cooling the inspired air, alone or in combination. However, the human body has very effective thermoregulatory responses such as areterio-venous shunts, vasoconstriction, and shivering, that generally combine to make such surface cooling and cold breathing gases ineffective to control core body temperature. In situ blood temperature modification using a heat exchange catheter system was described in U.S. Pat. Nos. 5,486,208, 5,837,003 and 6,110,168, all to Ginsburg, the disclosures of which are incorporated herein by reference in their entireties.
A method to exchange heat between a device positioned in the esophagus and a proximately located thoracic vessel, such as the descending aorta, in order to increase or decrease the temperature of the blood flowing in the vessel was described in U.S. Pat. No. 5,531,776 to Ward et al., entitled “Non-Invasive Aortic Impingement and Core and Cerebral Temperature Manipulation Method,” the contents of which are incorporated herein by reference in their entirety. The device includes an esophageal balloon which can be enlarged to displace the wall of the esophagus toward the thoracic vessel. The esophageal balloon includes a heat transfer surface, and heat is exchanged between the heat transfer surface and the blood flowing through the vessel across the wall of the esophagus and the wall of the vessel. The inflation of the balloon within the esophagus, however, may block the esophagus with various problematic results, for example blockage of saliva drainage to the stomach, and may limit the duration of the temperature treatment.
Controlling body temperature through gastric lavage (which is sometimes referred to as stomach pumping) involves the cyclic application of a cooling fluid directly to the stomach. In gastric lavage, up to about 500 ml of cooled sterile water is delivered into the stomach under gravity through an orogastric tube. Some of the water is later aspirated. The direct application of fluid to the stomach, and an inability to aspirate much of the delivered water, may cause abdominal cramping, gastrointestinal irritation, and diarrhea. This method is also generally messy and not suited for use in many environments, for example hospitals or ambulances. This procedure may also be limited by the amount of fluid which may be delivered into the stomach, particularly where a patient is very sensitive to fluid overload such as a patient suffering a myocardial infarct.
Therefore, there continues to be a need to develop a convenient method of controlling body temperature, e.g., inducing hypothermia or otherwise reducing the body temperature, or gently and slowly raising the body temperature from a hypothermic state.